The invention relates to a fuel injector for injecting fuel into the combustion chamber of an internal combustion engine. A fuel injector of this kind comprises a nozzle needle, which is able to perform stroke motions and by the stroke motion of which at least one injection opening can be exposed or closed, and furthermore comprises a control valve for controlling the stroke motion of the nozzle needle. For this purpose, the nozzle needle is acted upon in the closing direction by a hydraulic pressure in a control chamber, which can be varied depending on the respective operating position of the control valve. If the hydraulic pressure in the control chamber decreases, the nozzle needle can open. If the hydraulic pressure rises, on the other hand, the nozzle needle is returned to its seat.
A fuel injector of this kind is disclosed by German Offenlegungsschrift DE 10 2007 060 395 A1. The fuel injector described in this document comprises an on-off valve for actuating an injection valve member. The on-off valve has a closing element, which can be controlled by a magnetic actuator comprising a magnet assembly and an armature. The armature is guided in such a way that it can move on a guide element adjoining the closing element. The guidance of the closing element is assumed by a guide pin accommodated in the guide element and in the closing element. The guide pin and the closing element delimit a pressure chamber, which is connected to the control chamber by a discharge channel. In the closed position of the on-off valve, the hydraulic pressure in the pressure chamber corresponds to the control pressure in the control chamber.
It is furthermore known that the operating behavior of fuel injectors is not constant over the service life thereof. For example, the opening and closing behavior can change due to wear on the moving and/or dynamically stressed components. However, since the opening duration of the nozzle needle has a decisive effect on the fuel quantity injected, it is important to detect such changes and to counteract them.
German Offenlegungsschrift DE 10 2007 063 103 A1 discloses a device for determining an operating behavior of an injection valve of an injection system of an internal combustion engine, which comprises a piezofilm sensor, which can be inserted into the injection valve to determine the closing time of the injection valve. By means of the piezofilm sensor, the impact of the valve needle on the valve seat thereof is advantageously determined. In this way, it is possible to detect whether a predicted time for the impact of the valve needle corresponds to the actual time of the impact. If a deviation is detectable, the control parameters of a control device for the injection system can be adapted accordingly, ensuring that the closing time corresponds to the desired time in future injection processes.
Starting from the abovementioned prior art, it is the underlying object of the present invention to indicate a fuel injector having a sensor arrangement for detecting the needle closing time that is of simple construction and can be produced at low cost.